Some multi-band or other tactical radios operate in the high frequency (HF), very high frequency (VHF) (for satellite communications), and ultra high frequency (UHF) bands. The range of multi-band tactical radios can operate over about 2 through about 512 MHz frequency range. Next generation radios should cover about 2.0 to about 2,000 MHz to accommodate high data rate waveforms and less crowded frequency bands. This high frequency transmit mode is governed by standards such as MIL-STD-188-141B. UHF standards, on the other hand, provide different challenges over the 225 to about 512 MHz frequency range, including short-haul line-of-sight (LOS) communication and satellite communications (SATCOM) and cable. This type of propagation can be obtained through different weather conditions, foliage and other obstacles making UHF SATCOM an indispensable communications medium for many agencies. Different directional antennas can be used to improve antenna gain and improve data rates on the transmit and receive links. This type of communication is typically governed in one example by MIL-STD-188-181B, which provides calculation for higher transmit power and lower receive noise figures and other waveforms.
The joint tactical radio system (JTRS) has different designs that use oscillators, mixers, switchers, splitters, combiners and power amplifier devices to cover different frequency ranges. These modulation schemes used for these types of systems can occupy a fixed bandwidth channel at a fixed frequency spectrum. The systems usually include a memory of a coded waveform, such as a phase shift keying (PSK), amplitude shift keying (ASK), frequency shift keying (FSK), quadrature amplitude modulation (QAM), or continuous phase modulation (CPM) with a convolutional or other type of forward error correction code, for example, represented as a trellis structure. It should be understood that PSK, ASK, QAM and non-continuous FSK are memoryless modulations. For these modulations to have memory, Trellis-coded Modulation would need to be used for each specific M-PSK, M-QAM, M-ASK modulation type.
Throughout the communication industry, a requirement exists to improve power and spectral efficiency of a given modulation type, such as the PSK, ASK, FSK, CPM and QAM. A current industry standard uses filtering and other methods to eliminate any unnecessary out-of-band energy and improve the spectral efficiency and various forward error corrections (FEC) schemes and improve the power efficiency. The primary limitation these schemes include is the receiver demodulation complexity.
It would be advantageous if the distance property of uncoded, transmitted bits could be increased while taking advantage of any underlying memory (coding) scheme of those bits/symbols which are most likely to be received in error.